1. Field of the Invention
The present invention relates to a reproduction speed conversion apparatus for converting a reproduction speed of video data and a reproduction speed of audio data into an identical reproduction speed.
2. Description of the Related Art
A reproduction speed conversion apparatus converts a reproduction speed of a compression-encoded audio data and a reproduction speed of a compression-encoded video data into a high reproduction speed or a low reproduction speed. Even when the reproduction speeds are thus converted, the reproduced sound is natural to the listener.
FIG. 5 shows a structure of a conventional reproduction speed conversion apparatus 500. The reproduction speed conversion apparatus 500 includes an audio decoding section 501, an audio reproduction speed conversion section 502, a video reproduction speed conversion section 503, and a video decoding section 504.
Hereinafter, an operation of the conventional reproduction speed conversion apparatus 500 for converting a reproduction speed of compression-encoded audio data and a reproduction speed of compression-encoded video data in compliance with the MPEG Standards to a speed 1.2 times the original reproduction speeds will be described.
The audio decoding section 501 receives compression-encoded audio data.
The audio decoding section 501 operates in accordance with, for example, the Dolby AC3 or dts system adopted by the DVD-Video Standard, the MPEG1-layer II system adopted by the CS Digital Standard, MPEG2-AAC system adopted by the BS Digital Standard, the MLP system adopted by the DVD-Audio Standard, or the MP3 (MPEG1-layer III) system commonly used on the Internet.
The audio decoding section 501 decodes the compression-encoded audio data so as to output the decoded audio data. The audio reproduction speed conversion section 502 thins out repeated-waveform portions from the decoded audio data so as to convert the reproduction speed of the decoded audio data into a reproduction speed 1.2 times the original speed.
The video reproduction speed conversion section 503 receives compression-encoded video data in compliance with the MPEG Standards. The compression-encoded video data contains B-Picture, which is differential video data in compliance with the MPEG Standards. The video reproduction speed conversion section 503 thins out the B-Picture so as to convert the reproduction speed of the compression-encoded video data into a reproduction speed 1.2 times the original speed.
The video decoding section 504 decodes the compression-encoded video data so as to output the decoded video data.
The video decoding section 504 operates in accordance with, for example, the MPEG1, MPEG2, or MPEG4 system.
The compression-encoded audio data and the compression-encoded video data may be loaded from a storage device to a data load device.
FIG. 6 shows a structure of another conventional reproduction speed conversion apparatus 600. The reproduction speed conversion apparatus 600 includes a storage device 606 and a data load device 607 in addition to the elements included in the reproduction speed conversion apparatus 500.
The storage device 606 stores compression-encoded audio data and compression-encoded video data in compliance with the MPEG Standards. The compression-encoded audio data and the compression-encoded video data are loaded from the storage device 606 to the data load device 607.
An audio decoding section 601 receives compression-encoded audio data loaded from the storage device 606.
A video reproduction speed conversion section 603 receives the compression-encoded video data in compliance with the MPEG Standards loaded from the storage device 606.
The data load device 607 receives, from the video reproduction speed conversion section 603, a signal representing a reproduction speed obtained by the video reproduction speed conversion section 603, i.e., a reproduction speed 1.2 times the original reproduction speed. Upon receipt of this signal, the data load device 607 loads the compression-encoded audio data and the compression-encoded video data from the storage device 606. Thus, the quantity of the compression-encoded audio data and the compression-encoded video data which are output from the data load device 607 are not in excess or insufficient even when the reproduction speed of the decoded audio data and the reproduction speed of the compression-encoded video data are converted into a reproduction speed 1.2 times the original speeds.
FIG. 7 shows a structure of still another conventional reproduction speed conversion apparatus 700. The reproduction speed conversion apparatus 700 includes an audio decoding section 701, an audio reproduction speed conversion section 702, a video reproduction speed conversion section 703, a video decoding section 704, and an audio video synchronization section 705.
Hereinafter, an operation of the conventional reproduction speed conversion apparatus 700 for converting a reproduction speed of compression-encoded audio data and a reproduction speed of compression-encoded video data in compliance with the MPEG Standards to a speed 1.2 times the original reproduction speeds will be described.
The audio decoding section 701 receives compression-encoded audio data.
The audio decoding section 701 decodes the compression-encoded audio data so as to output the decoded audio data. Upon receipt of audio decoding timing data which represents a timing for decoding the compression-encoded audio data, the audio decoding section 701 decodes the compression-encoded audio data, so as to output the decoded audio data. The audio decoding timing data is output from the audio video synchronization section 705.
The audio reproduction speed conversion section 702 thins out repeated-waveform portions from the decoded audio data so as to convert the reproduction speed of the decoded audio data into the reproduction speed 1.2 times the original speed.
The video reproduction speed conversion section 703 receives compression-encoded video data in compliance with the MPEG Standards. The compression-encoded video data contains B-Picture, which is differential video data in compliance with the MPEG Standards. The video reproduction speed conversion section 703 thins out the B-Picture so as to convert the reproduction speed of the compression-encoded video data into a reproduction speed 1.2 times the original speed.
Upon receipt of video decoding timing data which represents a timing for decoding the compression-encoded video data, the video decoding section 704 decodes the-compression-encoded video data, so as to output the decoded video data. The video decoding timing data is output from the audio video synchronization section 705.
The audio video synchronization section 705 receives an audio time stamp which represents a time for reproducing the decoded audio data and a video time stamp which represents a time for reproducing the decoded video data.
In accordance with the audio time stamp and the video time stamp, the audio video synchronization section 705 synchronizes the timing for reproducing the decoded video data and the timing for reproducing the decoded audio data with each other.
In response to the audio time stamp, the audio video synchronization section 705 generates audio decoding timing data. As described above, the audio decoding section 701 decodes the compression-encoded audio data in response to the audio decoding timing data.
In response to the video time stamp, the audio video synchronization section 705 generates video decoding timing data. As described above, the video decoding section 704 decodes the compression-encoded video data in response to the audio decoding timing data.
The compression-encoded audio data and the compression-encoded video data may be loaded from a storage device to a data load device.
FIG. 8 shows a structure of still another conventional reproduction speed conversion apparatus 800. The reproduction speed conversion apparatus 800 includes a storage device 806 and a data load device 807 in addition to the elements included in the reproduction speed conversion apparatus 700.
The storage device 806 stores compression-encoded audio data, compression-encoded video data in compliance with the MPEG Standards, an audio time stamp, and a video time stamp. The compression-encoded audio data, compression-encoded video data in compliance with the MPEG Standards, an audio time stamp, and a video time stamp are loaded from the storage device 806 to the data load device 807.
An audio decoding section 801 receives compression-encoded audio data loaded from the storage device 806.
A video reproduction speed conversion section 803 receives the compression-encoded video data in compliance with the MPEG Standards loaded from the storage device 806.
An audio video synchronization section 805 receives the audio time stamp and the video time stamp which are loaded from the storage device 806.
The data load device 807 receives, from the audio reproduction speed conversion section 802, a signal representing a reproduction speed obtained by the audio reproduction speed conversion section 802, i.e., a reproduction speed 1.2 times the original reproduction speed. Upon receipt of this signal, the data load device 807 loads the compression-encoded audio data, the compression-encoded video data, the audio time stamp, and the video time stamp from the storage device 806. Thus, the quantity of the compression-encoded audio data, the compression-encoded video data, the audio time stamp, and the video time stamp which are output from the data load device 807 are not in excess or insufficient even when the reproduction speed of the decoded audio data and the reproduction speed of the compression-encoded video data are converted into a reproduction speed 1.2 times the original speeds.
The storage device 606 and the storage device 806 are each, for example, a hard disc. For recording audio data and video data on a hard disc built into a recording and reproduction apparatus, the audio data and the video data are encoded and then the compression-encoded audio data and the compression-encoded video data are recorded on the hard disc. As a system for reproducing the recorded compression-encoded audio data and compression-encoded video data only by the recording and reproduction apparatus, a system of the apparatus' own specifications may be adopted. For example, a system of recording compression-encoded audio data containing B-Picture on the hard disc at an arbitrary ratio may be adopted. Alternatively, a recording system obtained by combining the MPEG Standards and a unique technique may be adopted, by which a greater quantity of data is recorded on the hard disc for a sequence including rapidly-changing scenes and a smaller quantity of data is recorded on the hard disc for a sequence including less rapidly-changing scenes.
As described above, there is conventionally a premise that a recording and reproduction apparatus for recording audio data and video data is identical with a recording and reproduction apparatus for reproducing audio data and video data. Owing to this premise, the reproduction speed conversion apparatus 500, 600, 700 or 800 included in the recording and reproduction apparatus can convert the reproduction speed of the audio data and the reproduction speed of the video data into an identical reproduction speed.
However, the conventional reproduction speed conversion apparatuses 500, 600, 700 and 800 may not be able to convert a reproduction speed of audio data and a reproduction speed of video data which are recorded on a pre-authored recording medium (for example, a DVD-Video medium) or a recording medium possibly having data thereon recorded by another recording apparatus (for example, a DVD-RAM medium). The reason is that since the MPEG Standards for video data provide a high degree of freedom for reproduction speed, video data recorded by a recording apparatus produced by company A cannot always be reproduced by a reproduction apparatus produced by company B.
For example, when converting a reproduction speed of video data into a reproduction speed corresponding to the requested level by thinning out B-Picture, the ratio at which B-Picture appears needs to satisfy the requested level.